1. Field of the Invention
The present invention generally relates to a gas supplying method and a semiconductor manufacturing apparatus.
2. Description of the Related Art
In manufacturing a semiconductor, proposed is a “pulse control of a gas flow rate” with which a process gas having two different flow rate values are each switched by several seconds and repeatedly supplied at a time of supplying the process gas containing at least one gaseous species into a process space (see Japanese Laid-Open Patent Publication No. 2011-165769 and U.S. Pat. No. 8,440,473). As an example of the pulse control of the gas flow rate, the flow rate value of a gas A is set to be different from the flow rate value of a gas B and the gases A and B are alternately supplied like a pulse. As another example of the pulse control of the gas flow rate, the flow rate value of the gas A is set to have two different flow rate values and the two different flow rate values of the gas A are alternately switched over like a pulse in supplying the gas A. By performing the pulse control of the gas flow rate, so-called micro-loading, an etching rate is changed depending on sizes of a hole size or a trench size.
However, in a gas control method of switching between two different flow rate values, i.e., a flow rate value on a high flow rate side (hereinafter, a high flow rate value) and a flow rate value on a low flow rate side (hereinafter, a low flow rate value), a long time is required to reach the high flow rate value or the low flow rate value after switching from the low flow rate value or the high flow rate value, respectively. Therefore, as illustrated in FIG. 1, the actually supplied gas cannot reach a set flow rate during rising and falling after switching the gases. Therefore, a control for switching to a next gas flow rate occurs before reaching the set flow rate value. Thus, the gas flow rate of the actually supplied gas becomes lower than a preset gas flow rate, and there may occur a case where a predetermined property is not obtainable for a processed substrate.